It looks like an ordinary rubber strip, but I can't figure out why such a short piece would be joined in the middle, as it appears to be. I recently came across a web shop for car builders, and they seem to stock a few different types of rubbers and trims. I suggest you search their catalog:

I know this is rather late but I have just found the ideal replacement part for the black edge strip that goes across the rear of the car above the rear lights (assuming you did not find a genuine Matra spare part)

A friend was putting new tiles on my bathroom wall and he used a plastic edge strip that is the same size and shape as the Bagheera trim piece.

The piece I purchased for trial purposes is made by:-Homelux,Airfield Industrial Estate,Ashbourne,Derbyshire,DE8 1HA